An efficient ribosomal frame-shifting signal in the polymerase-encoding region of the coronavirus IBV.

Abstract

The polymerase‐encoding region of the genomic RNA of the coronavirus infectious bronchitis virus (IBV) contains two very large, briefly overlapping open reading frames (ORF), F1 and F2, and it has been suggested on the basis of sequence analysis that expression of the downstream ORF, F2, might be mediated through ribosomal frame‐shifting. To examine this possibility a cDNA fragment containing the F1/F2 overlap region was cloned within a marker gene and placed under the control of the bacteriophage SP6 promoter in a recombinant plasmid. Messenger RNA transcribed from this plasmid, when translated in cell‐free systems, specified the synthesis of polypeptides whose size was entirely consistent with the products predicted by an efficient ribosomal frame‐shifting event within the overlap region. The nature of the products was confirmed by their reactivity with antisera raised against defined portions of the flanking marker gene. This is the first non‐retroviral example of ribosomal frame‐shifting in higher eukaryotes.

Stop making sense or Regulation at the level of termination in eukaryotic protein synthesis

“…Several natural frameshifts have been described in prokaryotes and eukaryotes and recently reviewed ( [43], table 2). In eukaryotes, frameshift is required for the expression of retroviruses and related systems [43] and for the expression of a coronavirus [44]. In some cases as discussed below, the frameshifted products have been characterized by protein sequencing and the site of frameshift localized.…”

“…Another non-retroviral-like case should be mentioned: the -1 frameshift occurring in a coronavirus, IBV, for the synthesis of the Fl-F2 fusion protein, presumably encoding the putative viral polymerase [44].…”

“…Constructs containing the homopolymeric sequences alone do not induce frameshift, as suggested by experiments in which the short putative frameshift window was inserted upstream of an out-of-frame reporter gene [44,52,54]. One cannot exclude the possibility that downstream sequences of the reporter gene exert a negative effect on frameshifting.…”

“…Convincing stem and loop structures can be drawn downstream of the gag/p01 junction of HIV-l [52] and of the Fl/F2 junction of IBV [44]. They are also present downstream of the gag/X-pro junction of BLV, MMTV, HTLV I and II as well as downstream of the X-pro/pa/ junction of MMTV [54].…”

Analysis of a 9.6 kb sequence from the 3' end of canine coronavirus genomic RNA

“…Only this unique region of each mRNA is translated (reviewed by Spaan et al, 1988), thus the mRNAs are, in principle, functionally monocistronic. Nevertheless, some mRNAs contain two or more coding regions within the unique sequence and thus may be functionally bi-or tricistronic (Brierley et al, 1987;Liu et al, 1991 ;Liu & Inglis, 1992). The CCV virion is known to contain at least four protein species: the 204K spike glycoprotein, S; the 32K membrane glycoprotein, M; the 9.2K small membrane The nucleotide sequence data reported in this paper have been submitted to GenBank and EMBL and assigned the accession number D13096.…”